Nylon 6 catalyst system

ABSTRACT

A catalyst composition for the polymerization of Nylon 6 from caprolactam comprising a primary catalyst which comprises an alkali metal hypophosphite or an alkaliearth metal hypophosphite, and an organic phosphite cocatalyst. The catalyst composition of this invention is most useful when used in conjunction with the reactive extrusion technology which requires a very fast polymerization rate to take full advantage of this evolving technology.

BACKGROUND OF THE PRESENT INVENTION

The present invention relates to a catalyst composition for theproduction of Nylon 6 which comprises an alkali metal hypophosphite andan organic phosphite. More particularly, the present invention relatesto a catalyst composition comprising an alkali metal hypophosphite asthe primary catalyst and an organic phosphite as a cocatalyst, toincrease the rate of polymerization of Nylon 6.

Nylon 6 has been widely used as fibers and engineering plastics. In itsapplication as engineering plastics, Nylon 6 can be used for makingautomobile parts, electric and electronic components, electric wirecoatings, tool boxes, and coasters. As fibers, Nylon can be used inmaking fishing nets, carpets, tires and brushes (including toothbrushes,cosmetic brushes and grinding brushes) as well as stockings.

Nylon 6 can be synthesized using the conventional continuous reactionprocess, such as the V.K. Tower process, or the reactive extrusionprocess, which was developed only recently. In reactive extrusionprocess to synthesize polymers, the extruder is used as a mini-reactor.First, monomers, co-monomers and/or prepolymers are charged into theextruder. The reactants react inside the extruder to produce the polymermaterial, which is then extruded from the extruder to provide the finalproduct.

The reactive extrusion technology has the following advantages: First,it provides a high area-to-volume ratio for excellent heat transfer.Second, it provides excellent mixing action during the polymerizationreaction. This is particularly advantageous for highly viscous fluids,which can also be transported through the reactor. Third, it can beadapted to provide multiple temperature zones, each having a distincttemperature. Fourth, the reactive extruder can be adapted to providemultiple exhaust or vacuum sections, each vacuum section can have thesame or different of vacuum. Fifth, it involves a continuousreaction-extrusion process. Sixth, the resident time involved in theprocess is very short; therefore, the productivity can be very high perunit time. Seventh, the reactive extrusion process requires a muchsimpler apparatus than most other conventional commercial reactors.Finally, with the reactive extrusion process, the composition of thefeed monomers can be conveniently varied; this greatly enhances theutilization efficiency of the capital investment, and is particularlyadvantageous for production lines that make relatively small quantitiesof a large variety of products.

With the above mentioned advantages, the reactive extrusion technologypotentially can become one of the best methods to produce polymers andcopolymers. However, when the reactive extrusion technology is appliedto the polymerization of Nylon 6, current catalyst systems do notprovide fast enough reaction rate to take full advantage of thisevolving technology. The reaction must be very fast so that thepolymerization reaction to make Nylon can be completed in the extruderbefore they are extruded.

PRIOR ART

Sodium hypophosphite has been widely used as a catalyst for thepolymerization of polyamide. For example, Japanese Pat. App. JP 78-62205discloses a method to make polyamide using sodium hypophosphite ascatalyst. Japanese Pat. App. JP 89-179534 discloses the manufacturing ofpolyamides containing hexamethyleneterephthalamide units using sodiumhypophosphite as catalyst. Japanese Pat. App. JP 89-263892 disclosesaromatic copolyamides prepared in the presence of sodium hypophosphite.

Polymerization additives containing other than sodium hypophosphite havealso been reported. Japanese Pat. App. JP 89-70404 discloses the use ofsodium hypophosphite and MeOH during the polymerization ofhigh-molecular weight hexamethylene-terephthalamide polymers. InJapanese Pat. App. 87-28152, the additives further containalkylenediamine and monocarboxylic acids or primary or secondarymonoamines. Canadian Pat. No. 963594 discloses heat-stable nylon 66fibers with improved dyeability by adding sodium hypophosphite anddiphenylamine into the nylon salt solution before polymerizationreaction. Japanese Pat. App. JP 89-191926 discloses polyamidecompositions with good resistance to flame and heat. Alkaline earthmetal hypophosphites are used as catalyst in the polymerizationreaction. U.S. Pat. No. 4,113,708 discloses a method usingphenylphosphinic acid to reduce the formation of ammonia during the meltpreparation of polyamide. Ger. Offen. DE 2158014 discloses a method tostabilize nylon 66 by adding alkali metal hypophosphite into amides andadipate before polymerization. Japanese Pat. Apps. JP 89-179,534 and JP90-111015 disclose a method for the manufacturing of polyamides by firstpolymerizing diacids with diamine in the presence of a hypophosphite togive an oligomer then melt polymerizing the oligomer in the presence ofa polyethylene was. Great Britain Pat. App. GB 6648485 discloses a heatand light stabilizing additive for polyamide by adding sodiumhypophosphite and phenols containing at least one hydrocarbon radicaland a radical containing a COOH group or a derivative, to polyamideafter or during polycondensation. In Japanese Pat. App. JP 89-212160,the polymerization additives contain manganese hypophosphite,hexamethylenediamine, and triazine compounds, which are added toreactants as fire retardants.

Hypophosphites have also been used as additives to modify the propertiesof polyamide and/or copolyamide after the completion of thepolymerization reaction. U.S. Pat. No. 2,510,777 teaches a modifiedpolyamide having improved stability at elevated temperatures byincorporating into the polyamide a minor amount by weight ofhypophosphorous compound. Eur. Pat. App. EP 90-101760 disclosespolyamide compositions with improved oxidative stability; the additivesdisclosed therein including a low-temperature antioxidant from ahalogenated hydroxyl ammonium compound, hydrosulfide, bisulfite,phosphorus, and phosphate and a reducing agent from metal hypophosphiteand ammonium hypophosphite. Ger. Offen. DE 3636023 discloses agranulated thermoplastics for hot-melt adhesives by mixing copolyamideswith refined paraffin and sodium hypophosphite. Japanese Pat. App. JP85-198900 discloses a polyamide resin composition by blending polyamideswith modified polyolefin resins and metal salts of H₃ PO₄, H₃ PO₃ and H₃PO₂. Japanese Pat. App. JP 81-34897 discloses a method forsurface-sensitizing polyamide with sodium hydroxide and sodiumhypophosphite. Japanese Pat. App. JP 78-97229 discloses using sodiumhypophosphite as a heat stabilizer for copolyamide. Belg. BE 875530discloses nonflammable polyester, polyamide and polyester-polyamidecompositions by mixing polymers or copolymers with phosphinate salts.Japanese Pat. App. JP 90-208135 discloses a polyhexamethyleneadipamidewith restricted three-dimensional structure. Copper acetate, potassiumiodide or sodium hypophosphite is added to the final polymerized productas stabilizers. Japanese Pat. App. JP 90-116874 discloses mixing ofsodium hypophosphite or calcium acid hypophosphite with polyamide, toprevent discolorization. Japanese Pat. App. JP 88-331806 discloses theuse of hypophospherous acid or hypophosphite as anti-coloring agent forpolyamide fillers. Japanese Pat. App. JP 88-273373 discloses aninjection moulded aliphatic polyamide container comprising a polyamideand additives selected from orthophosphorous acid, hypophosphorous acid,alkali metal salts and alkaline salts. Eur. Pat. App. EP 88-305493discloses a method by which sodium hypophosphite and a cross-linkingagent are added to a linear aliphatic polyamide to improve its meltviscosity.

Examples of prior art literature disclosing the use of reactiveextruders include U.S. Pat. No. 4,603,166 which teaches a crystallinepolyamide composition prepared from aliphatic diamines and eithermixtures of terephathalic acid and adipic acid or mixtures ofterephathalic acid, isophthalic acid and adipic acid. Sodiumhypophosphite was used as catalyst. Ger. Offen. DE 3605202 discloses amethod for making high viscosity polyamide using a twin screw extruder.A prepolymer melt is made to travel through zones of elevated andreduced pressure which undergoes polycondensation in the extruder. Inthe high pressure zones, the melt is exposed to superheated steam and inthe reduced pressure zones, condensation water and steam are removedfrom the melt.

SUMMARY OF THE PRESENT INVENTION

The main object of the present invention is to provide catalystcompositions comprising alkali metal hypophosphites as primary catalystand an organic phosphite as cocatalysts so that the reaction rateassociated with the polymerization of Nylon 6 can be increased overthose using prior art catalysts.

The amount of primary catalyst is 0.01 to 5 parts per one hundred partsof caprolactam. The amount of organic phosphite cocatalyst is 0.01 to 5parts per one hundred of caprolactam. This results in a ratio betweenthe organic phosphite catalyst and primary catalyst that can range frombetween 0.002 and 500.

The present invention discloses catalyst compositions comprisinghypophosphites of alkali metals as primary catalyst and an organicphosphite as cocatalyst to increase the polymerization rate of Nylon 6.Nylon 6 is polymerized from caprolactam monomer.

The present invention discloses using organic phosphites as novelcocatalysts which can be selected from following groups:

1. General type phosphites which are represented by the followingstructure: ##STR1## wherein R₁, R₂, and R₃ can be, independently,aliphatic groups or aromatic groups, having 1 to 24 carbons, preferably4 to 18 carbons. One or two of R₁, R₂ and R₃ can be aliphatic groups andthe rest are aromatic groups. The aromatic groups can be naphthalene,benzene or derivatives of benzene or naphthalene, preferably thederivatives of naphthalene or benzene. Examples of the general types ofphosphites include diisodecyl pentaerythritol phosphite, triisodecylphosphite, triisooctyl phosphite, trilauryl phosphite, tristearylphosphite, trimethyl phosphite, triethyl phosphite, trinonylphenylphosphite, tris-(2,4-di-tert-butyl-phenol) phosphite,tris-(2,4-dimethylphenol) phosphite, tributyl phosphite, trioctylphosphite, triisooctyl phosphite, isooctyl diphenyl phosphite,diisooctyl phenyl phosphite, didecyl phenyl phosphite, decyl diphenylphosphite, didodecyl phenyl phosphite, dodecyl diphenyl phosphite,dodecyl dioctyl phosphite, decyl dioctyl phosphite,di(2,4-di-tert-butylphenyl) dodecyl phosphite,di(2,4-di-tert-butylphenyl) octyl phosphite, 2,4-di-tert-butyl-phenyldiisooctyl phosphite, dinonylphenyl decyl phosphite and diisodecylnonylphenyl phosphite.

2. Hindered type phosphites represented by the following structure:##STR2## wherein n is an integer from 1 to 10, preferably from 1 to 4.R₄ and R₅ can be, independently, aliphatic or aromatic groups having 1to 24 carbons, preferably 1 to 18 carbons. One of R₄ and R₅ can be analiphatic group and the other can be an aromatic group. The aromaticgroups can be naphthalene, benzene or the derivatives of naphthalene orbenzene, preferably derivatives of benzene or naphthalene. Examples ofthe hindered types of organic phosphites include phosphorous acid cyclicneopentanetetrayl dioctadecyl ester, phosphorous acid cyclicneopentanetetrayl dioctyl ester, phosphorous acid cylicneopentanetetrayl didecyl ester, phosphorous acid cyclicneopentanetetrayl dihexyl ester, phosphorous acid cyclicneopentanetetrayl bis (2,4-di-tert-butylphenyl) ester, phosphorous acidcyclic neopentanetetrayl bis (2,4,6-tri-tert-butylphenyl) ester,phosphorous cyclic neopentanetetrayl bis (2-tert-butylphenyl) ester,phosphorous acid cyclic neopentanetetrayl bis (2,6-di-tert-butylphenyl)ester, phosphorous acid cyclic neopentanetetrayl octyl2,6-di-tert-butylphenyl ester, phosphorous acid cyclic neopentanetetrayldecyl 2,6-di-tert-butylphenyl ester, phosphorous acid cyclicneopentanetetrayl distearyl ester, phosphorous acid cyclicneopentanetetrayl diphenyl ester, phosphorous acid cyclicneopentanetetrayl phenyl 2,4-di-tert-butylphenyl ester, and phosphorousacid cyclic neopentanetetrayl phenyl decyl ester.

The present invention will be substantially illustrated in the followingexamples. It should be noted that these examples are intended only toaid the understanding of this invention; it should further be understoodthat the scope of this invention, which is intended to be determined bythe appended claims, is by no means limited by these examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 (Preparation of Nylon6 Prepolymer)

The reactants comprised a predetermined amount of caprolactam, 2 PHR(parts per hundred parts of resin reactants) of water, and 0.1 PHR ofsodium hypophosphite. After the reactants were charged into the reactor,nitrogen gas was introduced into the reactor several times to purge airfrom the reactor. Then the reactor was closed and the temperature of thereactor was maintained at 270° C. for 30 min. During the reaction, ifthe pressure inside the reactor exceeded 7 Kg/cm², then the pressurewould be released to 3 Kg/cm². Subsequently, the reactor temperature wasreduced to 240° C. and the reactor pressure was released to 0 Kg/cm²,and the material was removed from the reactor. This completed thepolymerization reaction. After the polymerization reaction, Nylon 6prepolymer was produced which has a relative viscosity of 1.97. Therelative viscosity assumed that the viscosity of concentrated sulfuricacid (more than 96%) is 1 g/dl in a Cannon Ubbelohde Size 200 (B194)capillary viscometer at 30° C.

EXAMPLE 2 (Prior Art)

0.3 g to 0.4 g of the Nylon 6 prepolymer from Example 1. were added intoa stainless steel tube reactor. Seal the stainless steel tube reactor,and place the reactor into tin bath at 340° C. for 12 minutes. Theinternal temperature of the reactor is approximately 260° C. Theinternal pressure of the reactor is approximately 73 cm Hg (76 cm Hgbeing absolute vacuum). Remove the reactor from tin bath and cool thereactor in the air for 1 minute. Then cool the reactor with water untilthe temperature of the reactor reached room temperature. Open thereactor to remove the sample. The product is a Nylon 6 polymer. Measurethe relative viscosity of the sample. The relative viscosity of thepolymer is 3.93.

EXAMPLE 3 (This Invention)

Prepare the Nylon 6 prepolymer which is synthesized according to themethod described in Example 1, and all the reaction conditions are thesame as those in Example 2, except that 0.5 PHR various types of organicphosphites were added into the reactor. The compositions of the organicphosphite cocatalysts are listed in Table 1. After the reaction iscompleted according to the method described in Example 2, the relativeviscosity is measured. The product is a Nylon 6 polymer.

The relative viscosities of reaction products from Examples 1 through 3are listed in Table 2. The relative viscosities of the Nylon 6 polymersthat are synthesized using an organic phosphite as cocatalyst are higherthan those without the organic phosphite cocatalyst, indicating a morecomplete reaction within the same reaction time by the addition of theorganic phosphite cocatalyst disclosed in this invention.

                  TABLE 1                                                         ______________________________________                                        Example                                                                       No.    Cocatalyst Composition                                                                            Type                                               ______________________________________                                        3-A    Triisodecyl phosphite                                                                             general type organic                                                          phosphite                                          3-B    Trinonylphenyl phosphite                                                                          general type organic                                                          phosphite                                          3-C    Isooctyl diphenyl phosphite                                                                       general type organic                                                          phosphite                                          3-D    Phosphorous acid cyclic neo-                                                                      hindered type                                             pentanetetrayl di-octadecyl ester                                                                 organic phosphite                                  3-E    Phosphorous acid cyclic neo-                                                                      hindered type                                             pentanetetrayl bis-(2,4-di-tert-butyl-                                                            organic phosphite                                         phenyl) ester                                                          ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Example                                                                              Polymer                 Relative                                       No.    Composition             Viscosity                                      ______________________________________                                        1      Nylon 6 prepolymer      1.97                                           2      Nylon 6 polymer (w/o cocatalyst)                                                                      3.93                                           3-A    Nylon 6 polymer (with organic phosphite)                                                              5.43                                           3-B    Nylon 6 polymer (with organic phosphite)                                                              4.82                                           3-C    Nylon 6 polymer (with organic phosphite)                                                              5.30                                           3-D    Nylon 6 polymer (with organic phosphite)                                                              4.51                                           3-E    Nylon 6 polymer (with organic phosphite)                                                              5.00                                           ______________________________________                                    

EXAMPLE 4 (Preparation of Nylon 6 Prepolymer)

The reactants and reaction conditions were the same as those in Example1, except that the reaction was maintain at 270° C. for 20 minutes,instead of the 30 min as in Example 1. The relative viscosity of theNylon 6 prepolymer was 1.82.

EXAMPLE 5 (Prior Art)

Grind the Nylon 6 prepolymer from Example 4 into powders, and feed thepowder into a twin screw extruder (W & P ZSK 30 model, with a diameterof 30 mm and an L/D of 27). Then extrude the reactants. The conditionsof extrusion are described in the following paragraph.

The reaction temperatures are 265° C. in the first section, 280° C. inthe second, third, and fourth sections, and 270° C. in the fifthsection. The temperature of the die is 270° C. The pressure in thefourth section is 72 cm Hg (76 mm Hg being absolute vacuum). Therotation speed of the screw is 100 rpm, representing an average residenttime of about two minutes.

EXAMPLE 6 (This Invention)

The reactants are Nylon 6 prepolymer from Example 4 and 0.3 PHR ofphosphorous acid cyclic neopentanetetrayl bis(2,4-di-tert-butylphenyl)ester, a hindered organic phosphite. All the other conditions are thesame as those in Example 5. The relative viscosities of reactionproducts from Examples 4 through 6 are listed in Table 3. The relativeviscosities of the Nylon 6 polymer that was synthesized using theorganic phosphite as cocatalyst higher than that without the organicphosphite cocatalyst.

                  TABLE 3                                                         ______________________________________                                        Example                        Relative                                       No.    Polymer Composition     Viscosity                                      ______________________________________                                        4      Nylon 6 prepolymer      1.82                                           5      Nylon 6 polymer (w/o cocatalyst)                                                                      2.28                                           6      Nylon 6 polymer (with organic phosphite)                                                              2.62                                           ______________________________________                                    

From all the tables shown above, it is evident that the addition oforganic phosphite as a cocatalyst, in the presence of a primarycatalyst, increases the rate of polymerization of Nylon 6.

What is claimed is:
 1. A catalyst composition for the preparation ofNylon 6 from caprolactam, said catalyst composition comprising:(a) aprimary catalyst selected from the group consisting of alkali metalhypophosphites and alkali earth metal hypophosphites; (b) an organicphosphite cocatalyst selected from either compound I or compound IIwherein compound I is represented by the following structure: ##STR3##wherein R₁, R₂, and R₃ are selected, independently, from the groupconsisting of aliphatic and aromatic radicals, and compound II isrepresented by the following structure: ##STR4## wherein n is an integerfrom 1 to 10, and R₄, and R₅ are selected, independently, from the groupconsisting of aliphatic and aromatic radicals; (c) the ratio betweensaid organic phosphite cocatalyst and said primary catalyst is between0.002 and
 500. 2. The catalyst composition of claim 1 wherein saidalkali metal hypophosphite is sodium hypophosphite.
 3. The catalystcomposition of claim 1 wherein said organic phosphite cocatalyst isrepresented by the following formula: ##STR5## wherein R₁, R₂, and R₃are, independently, selected from the group consisting of aliphatic oraromatic radicals.
 4. The catalyst composition of claim 3 wherein saidaliphatic radicals contain 1 to 24 carbons.
 5. The catalyst compositionof claim 3 wherein said aliphatic radicals contain 4 to 18 carbons. 6.The catalyst composition of claim 3 wherein said organic phosphitecocatalyst is selected from the group consisting of diisodecylpentaerythritol phosphite, triisodecyl phosphite, triisooctyl phosphite,trilauryl phosphite, tristearyl phosphite, trimethyl phosphite, triethylphosphite, trinonylphenyl phosphite, tris-(2,4-di-tert-butyl-phenyl)phosphite, tris-(2,4-dimethylphenyl) phosphite, tributyl phosphite,trioctyl phosphite, triisooctyl phosphite, isooctyl diphenyl phosphite,diisooctyl phenyl phosphite, didecyl phenyl phosphite, decyl diphenylphosphite, didodecyl phenyl phosphite, dodecyl diphenyl phosphite,dodecyl dioctyl phosphite, decyl dioctyl phosphite,di-(2,4-di-tert-butylphenyl) dodecyl phosphite,di-(2,4-di-tert-butylphenyl) octal phosphite, 2,4-di-tert-butyl-phenyldiisooctyl phosphite, dinonylphenyl decyl phosphite and diisodecylnonylphenyl phosphite.
 7. The catalyst composition of claim 1 whereinsaid organic phosphite cocatalyst is represented by the followingstructure: ##STR6## wherein n is an integer from 1 to 10, and R₄ and R₅are, independently, selected from the group consisting aliphatic andaromatic radicals.
 8. The catalyst composition of claim 7 wherein n isan integer from 1 to
 4. 9. The catalyst composition of claim 7 whereinsaid aliphatic radicals contain 1 to 24 carbons.
 10. The catalystcomposition of claim 7 wherein said aliphatic radicals contain 1 to 18carbons.
 11. The catalyst composition of claim 7 wherein said organicphosphite cocatalyst is selected from the group consisting of cyclicneopentanetetrayl dioctadecyl ester, phosphorous acid cyclicneopentanetetrayl dioctyl ester, phosphorous acid cylicneopentanetetrayl didecyl ester, phosphorous acid cyclicneopentanetetrayl dihexyl ester, phosphorous acid cyclicneopentanetetrayl bis (2,4-di-tert-butylphenyl) ester, phosphorous acidcyclic neopentanetetrayl bis-(2,4,6-tri-tert-butylphenyl) ester,phosphorous cyclic neopentanetetrayl bis-(2-tert-butylphenyl) ester,phosphorous acid cyclic neopentanetetrayl bis-(2,6-di-tert-butylphenyl)ester, phosphorous acid cyclic neopentanetetrayl octyl2,6-di-tert-butylphenyl ester, phosphorous acid cyclic neopentanetetrayldecyl 2,6-di-tert-butylphenyl ester, phosphorous cyclicneopentanetetrayl distearyl ester, phosphorous acid cyclicneopentanetetrayl diphenyl ester, phosphorous acid cyclicneopentanetetrayl phenol 2,4-di-tert-butylphenyl ester, and phosphorousacid cyclic neopentanetetrayl phenol decyl ester.